Many attempts have been made in the prior art to provide product dispensers. One problem found in the prior art was that of "suck-back" wherein a portion of a partially dispensed product and also air is drawn inwardly into a product reservoir after the product dispenser has been operated. This often occurs, for example, where a prior art flexible walled container is used. After the flexible walled container has been squeezed to dispense the product, and then released, the return of the container to its memory position lowers the pressure within the container thereby drawing air and partially dispensed product back into the container. This problem is particularly pertinent where the product is damaged by oxidation and also where sterile products are important, for example, in hospitals.
Another problem found in many prior art dispensers is that it is often difficult in such dispensers to empty the product completely without relatively sophisticated dispensing equipment.
Still another problem found in many prior art dispensers is that the dispensers may only be utilized in certain positions. For example, if one uses a dispenser which relies primarily upon gravity, it is extremely difficult to use the dispenser in an upright position, while on the other hand, if an aerosol dispenser is utilized, in some positions it is possible to dispense the carrier fluid and not the desired product.
Many rather sophisticated prior art dispensers have been designed to attempt to solve one or more of the above problems. If the cost of the dispenser structure is too high, it becomes imperative to re-use such structure. On the other hand, many prior art throw-away dispensers create an additional ecology problem of garbage or trash disposal.
Roth U.S. Pat. No. 3,289,949 discloses the use of an inner cartridge which is pressurized. The product is dispensed by a venturi principle.
U.S. Pat. No. 3,876,115 is directed to a double expansible bladder container having two expansive bladders coextensive with one another. This dispenser relies upon the high-elastic memory material of the second bladder to dispense product from the coextensive first bladder.